1. Field of the Invention
The present invention relates generally to corneal contact lenses and their use in treating myopia. More particularly, the present invention is directed to corneal contact lenses which are shaped to provide gradual altering of the patients's cornea during continued wear to reshape the cornea to reduce the myopic condition.
2. Description of Related Art
Myopia, also known as nearsightedness, is a condition where the radius of curvature of the cornea is smaller than normal. Individuals with this condition have difficulty in focusing on distant objects because the cornea is curved too sharply to provide adequate focusing. Myopia is a common condition for which no entirely suitable permanent treatment has been developed.
One approach to correcting myopia is through surgical reshaping of the cornea. However, such surgical procedures have not been entirely proven and there is some question as to the permanency of the surgically altered lens shape.
Another approach is to alter the corneal shape by wearing corneal contact lenses which are designed to continually exert pressure on selected locations of the cornea to gradually force or mold the cornea into the desired normal corneal curvature. A retainer lens is then worn on a part time basis to prevent the cornea from returning to its original shape. This method of treatment is commonly referred to as orthokeratology. The success of any treatment by orthokeratology is dependent upon the shape and structure of the corneal contact lens.
My prior U.S. Pat. Nos. 4,952,045; 5,191,365; 5,349,395; and U.S Pat. No. 5,428,412 disclose corneal contact lenses which are examples of the types of lenses which have been designed for use in treating myopia. The lenses typically include a central zone, a tear zone located concentrically around the central zone and an outer peripheral zone which is located concentrically around the tear zone. This lens design provides a radius of curvature in the tear zone which is sharper than the radius of curvature for both the central zone and peripheral zones. This particular type of multi-curve corneal contact lens configuration is useful in changing the shape of the myopic cornea to that of a normally shaped cornea. In addition, the steeper curve of the tear zone provides a ring shaped area where fluid is concentrated between the lens and cornea. As the contact lens reshapes the cornea, the central portion of the cornea flattens and forces the para-central cornea to flow into the tear zone. As reshaping of the cornea occurs, a new flatter contact lens is re-fit. In most cases, if a flatter contact lens is not fit the lens may tighten and possibly adhere to the cornea.
Although the corneal contact lens of the type disclosed in my prior patents are well suited for their, intended purpose, there is continual need for improvement of the design of such lenses to make them better suited for use in treating myopia.